Penetration-type color tube with phosphors separated by conductive barrier layer

ABSTRACT

A plural-color cathodoluminescent screen for use in a cathoderay tube wherein at least two layers of light-emitting phosphors have therebetween a separation layer of electrically conductive oxide material that is substantially translucent to electromagnetic radiation and substantially opaque to the penetration of electron beams of predetermined velocity. The screen includes a nucleation to achieve the uniform disposition of an oxidizable metal which when subsequently heated forms the metallic oxide of the separation layer.

United States Patent lnventors Anthony V. Gallaro Auburn, N.Y.; WalterF. Kazult, Loves Park, llL; Kenneth Speigel, Seneca Falls, N.Y. Appl.No. 853,083 Filed Aug. 26, 1969 Division of Ser. No. 634,724, Apr.28,1967, Pat. No. 3,526,527.

Patented Sept. 7, I971 Assignee Sylvania Electric Products Inc.

PENETRATION-TYPE COLOR TUBE WITH PHOSPHORS SEPARATED BY CONDUCTIVEBARRIER LAYER 2 Claims, 3 Drawing Figs.

US. Cl t. 313/92 PF, 252/512 1m. (:1 .1101 j 29/28, H0lj3l/20,H0lj 29/20Field of Search 313/92, 92 PF 'EQQ I LOW VELOCITY OXIDIZED METAL PrimaryExaminerRobert Scgal Attorneys-Norman J. OMalley, Donald R. Castle andFrederick H. Rinn ABSTRACT: A plural-color cathodolulminescent screenfor use in a cathode-ray tube wherein at least two layers oflightemitting phosphors have therebetween a separation layer ofelectrically conductive oxide material that is substantially translucentto electromagnetic radiation and substantially opaque to the penetrationof electron beams of predetermined velocity. The screen includes anucleation to achieve the uniform disposition of an oxidizable metalwhich when subsequently heated forms the metallic oxide of theseparation layer.

HIGH VELOCITY ELECTRON BEAM 43,Q/ECTRON BEAM I r 1 l I l I I l5 I I I II I PATENTED sEP mm 3.503830 I 1 SCREEN SUPPORT QQ LOW VELOCITY F HIGHVELOCITY ELECTRON BEAM, \{L/ECTRON BEAM KENNETH SPEIGEL TD ATTORNEY 1PENETRATION-TYPE COLOR TUBE WITH-ll PHOSPHORS SEPARATE!) BY CONDUCTIVEBARRIER LAYER CROSS-REFERENCE TO RELATED APPLICATIONS This applicationis a divisional application of Ser. No. 634,724, filed Apr. 28, 1967,now US. Pat. No. 3,526,527,

. which is assigned to the assignee of the present invention. Thisdivisional application contains matter disclosed but not claimed inanother US. Pat. application filed concurrently herewith, whichapplication is also a division of Ser. No.

BACKGROUND OF THE INVENTION This invention. relates to beam-penetrationtypes of cathodoluminescent color screens and more particularly toscreens having different layers of color-emitting phosphors excited byelectron beams of differing velocities.

It is common in beam-penetration multilayer cathodolusilicon dioxide.Certain disadvantages have been noted in screens employing suchseparation or barrier layers, for instance, metal deposits of specificthicknesses sufficient to control the penetration by electron beams ofpredetermined velocities usually exhibit a degree of opacity whichlimits translucency to electromagnetic radiation. On the other hand,nonconductive silicon dioxide which is substantially translucent tolight energy, in addition to being difficult to uniformly deposit,manifests an undesirable dielectric property which momentarily retainsan electron charge at the point of beam impingement. For example, theelectron-charge-retention characteristic of the silicon dioxide layerslightly prolongs the excitation of the phosphor distal to the beamsource and temporarily imparts color impurity to the color emission ofthe lower velocity excitable phosphor proximal to the beam source.

OBJECTS AND SUMMARY OF THE INVENTION It is an object of the invention toreduce the aforementioned disadvantages and provide an improved beampenetration type of cathodoluminescent screen.

Another object is to provide a beam penetration cathode ray tube screenthat exhibits improved color purity of the low velocity beam-excitedcolor emission.

A furtherobject is the provision of a beam-penetration cathode ray tubescreen having a separation layer therein of improved uniformity.

The foregoing objects are achieved in one aspect of the in vention bythe provision of a cathode ray tube screen having therein at least twolayers of energy-emitting phosphor materials with a uniform separationlayer disposed therebetween.

Such separation layer is of an electrical conductive oxide substancethat is nondeleterious to the adjacent phosphor materials whileexhibiting opacity to a predetermined level of discrete phosphorexcitation energy and translucency to electromagnetic radiation. Anucleate of metal molecules dispersed over a first of the phosphormaterials enhances the deposition of a uniform coating of an oxidizablemetal thereover. The application of heat to the partial screen structurevolatilizes the heat-decomposable material and oxidizes the metalcoating to form the aforementioned separation layer. The second phosphormaterial is disposed over the separation layer.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a cross-sectional viewillustrating a partially formed cathode ray tube screen structure;

H6. 2 is a cross-sectional view showing the screen structure of FIG. 1after the baking step in screen processing; and

FIG. 3 is a fragmentary cross-sectional view of a cathode ray tubewherein the screen structure of the invention is formed on the innersurface of the viewing panel.

DESCRIPTION OF THE PREFERRED EMBODIMENT FOr a better understanding ofthe present invention, together with other and further objects,advantages and capabilities thereof, reference is made to the followingspecification and appended claims in connection with the aforedescribeddrawing.

With reference to the figures, there is shown a partially formedluminescent screen structure 11 which is formed on a substantiallytransparent support medium 13 such as a glass substrate or the innersurface of a cathode ray tube faceplate. The screen utilizes a pluralityof phosphors, of which at least one is responsive to electronexcitation. Additionally, a screen of this type may also include one ormore phosphors that are responsive to electromagnetic radiation emittedby a related electron-responsive phosphor. The process of forming thescreen comprises the application of a layer of a first phosphor material15 which is substantially translucent and capable of energy emissionupon excitation. This phosphor is disposed on the support medium by oneof several conventional techniques such as for example by the settlingof phosphor through a liquid cushion. Due to the range of phosphorparticle sizes comprising the first phosphor layer, a somewhat roughenedsurface results. It is important that the separation or barrier layer25, which is subsequently formed thereover, has a uniform thickness;therefore, a layer of a heat-decomposable material is applied in aconventional manner thereon to fill in the rough topography of thephosphor layer and provide a smooth surface thereover. Suitableheat-decomposable materials may be lacquer solutions such as methylmethacrylate dissolved in toluene which is appropriate for sprayapplication or nitrocellulose dissolved in :amyl acetate which issuitable for fioattype application. Upon drying, the lacquer filmprovides a smooth base on which the separation layer 25 is formed.

It has been found that a nucleation applied in the form of a dispersionof metal molecules enhances the adherence and uniform deposition of acompatible metal disposed thereover. The nucleated material ll9, being avery thin dispersion or molecular film, provides microscopic islands"which promote uniform adherence of the sequentially applied compatiblecoating of oxidizable metal 21 vaporized thereon.

Heating of the screen-support medium and the aforedescribed partiallyformed screen thereon is consummated at a time-temperature relationshipthat is not deleterious to the phosphor materials therein, butsufficient to volatilice and remove the heat-decomposable material andconvert the oxidizable metal to the oxide forming the separationlayer25. The metal oxide thus formed exhibits electrical conductivity,opacity to discrete phosphor excitation energy of a sub stantiallypredetermined level and translucency to electromagnetic radiationimpinged thereon. As used herein, the designation electromagneticradiation" is intended to include the scope of the electromagneticspectrum extending from gamma rays through infrared radiation. FIG. 2illustrates the partial screen structure 11' after heating, whichembodies the first phosphor and the separation layer of oxidized metal.Subsequently, a second phosphor material, capable of energy emissionupon excitation, is disposed upon the separation layer by a techniqueconventional to the art.

In greater detail, a luminescent screen such as a cathodoluminescentscreen having at least two electron-responsive phosphors therein, asutilized in a plural color cathode ray tube, will be described alongwith a process for fabricating the same. The aforerecited process asshown in FIGS. l and 2 is likewise applicable in this instance fordisposing the screen directly on the face panel surface of the tube.

With reference to FIG. 3, a cathode ray tube 31 is partially shownwherein means 35 for generating electron beams of predeterminedvelocities is shown. This source of beams comprises one or more electronguns oriented in spaced relationship to the improvedbeam-penetration-type cathodoluminescent screen 39 which is formed onthe inner surface of the tube face panel 13'. When a single-gun beamsource is employed, anode switching means is utilized to provide beamsof differing velocities, whereas in a plural gun source, separate gunsemanate lowand high-velocity beams respectively.

The first disposed phosphor layer 15' is in the form of anelectron-responsive color-emitting material such as the E.l.A. P-lphosphor (Zn,SiO :Mn) which is a green-emitting medium persistencematerial. This phosphor is disposed on the panel at a density range, inthis instance, of approximately 3 to 5 mg./cm.. Next, one of theaforementioned lacquer materials is spray-disposed thereover and thenucleate dispersed by vaporization thereon. The dispersion of thenucleate is of a minute thickness not deleterious to the translucency ofthe subsequently formed separation layer. it has been discovered that asuitable nucleating material is in the form of a metallic elementrequiring a vaporization temperature of at least 500 centigrade toconsummate the evaporation thereof at a pressure of Such metals include,for example, silver, tin, aluminum, and chromium. In this embodiment, amolecular dispersion of vaporized aluminum is utilized as the nucleatingmaterial.

Upon the nucleate, a uniform coating of at least one metallic elementselected from Groups lb to 4a inclusive of Periods IV and V of thePeriodic Table of Elements if vaporized thereon. Elements in thesedesignations have oxide forms that are electrically conductive,translucent to light energy and exhibit opacity to electron beams ofpredetermined velocities in relationship to the thickness of the oxidelayer. One of the Period V elements is, for example, cadmium which isutilized as the evaporated metallic coating in this embodiment of theinvention. The partially formed screen structure is heated toapproximately 400 C. for a time period of about 45 minutes to remove thelacquer material by volatilization and convert the cadmium deposition toa continuous separation layer 25' of electrically conductive cadmiumoxide having a uniformity of thickness. In this instance, the thicknessof the cadmium oxide is in the order of 900 Angstroms. The temperatureof the heating is not deleterious to the P-l phosphor contained in thescreen. It will be noted that the cadmium oxide separation layer 25'extends partially on the wall of the tube due to the deposition of thebasic materials; i.e., the lacquer being sprayapplied and the nucleatedaluminum and cadmium being vaporized thereon.

A layer of a second electron-responsive phosphor 27 such as E.l.A. P-22RE. Red (YVOgEu), a high-efficiency redemitting phosphor, is disposed ina conventional manner over the separation layer and is of asubstantially uniform density within the range of approximately 1 to 3mgJcm. A conductive coating 37, such as aquadag applied to the funneland neck portions of the tube, makes contact with the separation layerand provides the anode connective path. The cathodoluminescent screen sodescribed provides an outstanding twocolor display, the specificphosphors being excited to color emission by electron beams of differentvelocities.

The low-velocity electron beam 41, emanating from the beam-generatingsource, is in this instance in the order of 6 kv. which excites thesecond or red-emitting phosphor 27 to bright color emission but hasinsufficient velocity to penetrate through the separation layer 25'. Theluminous red emission thus produced traverses the optically translucentseparation layer and the optically translucent P-l phosphor to bevisible as a bright red display to the observer viewing the face panelof the tube.

The high-velocity beam 43 being, for example, in the order of 12 kv.excites the second or red-emitting phosphor and is of sufficientvelocity to traverse the separation layer and excite the first orgreen-emitting phosphor layer disposed on the face panel. Since, in thisinstance, it is desired that a green color be observed as a result ofhigh-velocity beam excitation,'the first or green-emitting phosphor isdisposed in an amount to insure predominance of the green emission overthe red therebeneath when the two are coincidentally excited by a commonbeam. Thus, from the viewpoint of the observer, distinct bright red andbright green displays are produced by the lowand high-velocity beamsrespectively. If the two beams are generated and directed tosimultaneously impinge upon contiguous screen areas, a brightcomplementary color combination results.

The composition of the substantially translucent and electricallyconductive separation or barrier layer 25 is important as theconductivity characteristic thereof readily dissipates thebeam-impingement charge thereon and provides twofold results notevidenced in nonconductive capacitance-prone separators. Firstly, thespot size of the red and green color emissions are both of a sizesmaller due to the absence of the capacitance characteristic whichnormally tends to retain some of the electron charge at the point ofbeam impingement causing the beam spot to bloom". Secondly, when a beamis switched from high-velocity to low-velocity operation, the electroncharge at the point of impingement is dissipated so that there is nodeleterious carryover of green excitation and emission to momentarilylend color impurity to the desired red emission from the second phosphorlayer. Hence the beneficial characteristics of the cadmium oxideseparation layer relate to its translucency which readily conveys theluminescent brightness of the second phosphor layer, and to itsconductivity which improves small spot size of both phosphor emissionsand color purity of the luminescence emitted by the second orred-emitting phosphor.

Thus, there is provided a beam-penetration type of cathodoluminescentscreen that exhibits improved brightness and color purity heretoforesought but not previously evidenced in the beam-penetration type ofcathode ray tube screen. The metallic nucleation advantageouslyfacilitates the uniform deposition of the improved separation layer andexpedites fabrication of the subject screen.

While there has been shown and described what is at present consideredthe preferred embodiment of the invention, it will be obvious to thoseskilled in the art that various changes and modifications may be madetherein without departing from the scope of the invention as defined bythe appended claims.

1. A cathode ray tube having means therein to generate a plurality ofelectron beams of predetermined velocities to impinge on a plural-colorcathodoluminescent screen formed on a related supporting surfacerelative to a viewing area thereof, said screen comprising:

a first electron-responsive phosphor material disposed in asubstantially uniform manner on said supporting surface;

a separation barrier layer formed of uniform thickness in overlayrelationship with said first phosphor material, said electron barrierseparation layer being electrically connected to the anode of said tubeand comprising molecular islands of a discontinuous metallic nucleationof aluminum upon which is disposed an electron barrier of anelectrically conductive oxide separation substance that is substantiallyopaque to the penetration of said electron beams of predeterminedvelocity, said electrically conductive separation material being anoxide of at least one metal selected from the group consisting ofsilver, cadmium and indium; and

a second electron-responsive phosphor material disposed on saidseparation barrier layer facing said electrongenerating means, theamount of said first phosphor being greater than the amount of saidsecond phosphor to provide a predominance of said first phosphoremission over that of said second phosphor emission when both phosphorsare excited by a common high-velocity beam, said intermediatelypositioned separation barrier layer being electrically conductivereadily dissipates the elecmomso tron charge from point of beamimpingement thereon to provide color purity of the luminescence emittedby said second phosphor.

2. A cathode ray tube having means therein to generate a plurality ofelectron beams of predetermined velocities to impinge on a plural-colorcathodoluminescent screen fonned on a related supporting surfacerelative to a viewing area thereof, said screen comprising:

a first electron-responsive phosphor material disposed in asubstantially uniform manner on said supporting surface;

a separation barrier layer formed of uniform thickness in overlayrelationship with said first phosphor material, said electron barrierseparation layer being electrically connected to the anode of said tubeand comprising molecular islands of a discontinuous metallic nucleationof aluminum, upon which is disposed an electron barrier of anelectrically conductive oxide separation substance in the form ofcadmium oxide that is substantially translucent to electromagneticradiation and opaque to the penetration of said electron beams ofpredetermined velocity; and second electron-responsive phosphor materialdisposed on said separation barrier layer facing said electrongeneratingmeans, said second phosphor having a color emission in substantially thered-related portion of the spectrum, said intermediately positionedseparation layer being electrically conductive readilly dissipates theelectron charge from point of beam impingement thereon to provide colorpurity of the luminescence emitted by said second phosphor @32 3 UNITEDSTATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,603,830Dated September 7 1971 Anthony V. Gallaro, Walter F. Kazuk, KennethSpeigel It is certified that error appears in the above-identifiedpatent and that said Letters Patent are hereby corrected as shown below:

1 Column 3, line 25 of the specification "1O should read "10 Column 3,line 31 of the specification "if" should read 1s Signed and sealed this7th day of March 1972.

(SEAL) Attest:

EDWARD M.PLETCHER,JR. ROBERT GOTTSCHALK Ahtesting Officer Commissionerof Patents

2. A cathode ray tube having means therein to generate a plurality ofelectron beams of predetermined velocities to impinge on a plural-colorcathodoluminescent screen formed on a related supporting surfacerelative to a viewing area thereof, said screen comprising: a firstelectron-responsive phosphor material disposed in a substantiallyuniform manner on said supporting surface; a separation barrier layerformed of uniform thickness in overlay relationship with said firstphosphor material, said electron barrier separation layer beingelectrically connected to the anode of said tube and comprisingmolecular islands of a discontinuous metallic nucleation of aluminum,upon which is disposed an electron barrier of an electrically conductiveoxide separation substance in the form of cadmium oxide that issubstantially translucent to electromagnetic radiation and opaque to thepenetration of said electron beams of predetermined velocity; and asecond electron-responsive phosphor material disposed on said separationbarrier layer facing said electron-generating means, said secondphosphor having a color emission in substantially the red-relatedportion of the spectrum, said intermediately positioned separation layerbeing electrically conductive readily dissipates the electron chargefrom point of beam impingement thereon to provide color purity of theluminescence emitted by said second phosphor.